In view of low-temperature properties, rubber components consisting only of natural rubber and polybutadiene rubber have been widely used in cap treads of cold weather tires. A further technique that has been used to improve performance on ice is to foam a rubber component (see Patent Literature 1).
Moreover, due to the recent improvement of road conditions, more and more vehicles with cold weather tires are driven at high speeds. However, since conventional cold weather tires place an importance on the performance on ice and snow achieved during running at relatively low speeds, they tend to show inferior handling stability and grip performance during high speed running.
Particularly in the case of fine particle silica-containing formulations, which are considered promising due to their properties such as abrasion resistance and fuel economy, it is difficult to control the distribution of fine particle silica between the polybutadiene rubber layer and the natural rubber layer and the dispersion thereof in the rubber layers. Thus, tires with such formulations tend to be greatly inferior in high speed performance on snow- and ice-free roads to summer tires.
Thus, a need exists for a technique to improve high speed performance (handling stability, grip performance) on snow- and ice-free cold roads while ensuring performance on ice and snow, thereby achieving a balanced improvement in properties including fuel economy, abrasion resistance, performance on ice and snow, and high speed performance (handling stability, grip performance) on snow- and ice-free cold roads.